In recent years, a transmission amount of an information and a transfer velocity of the information and telecommunications equipment such as a personal computer and a cellular mobile phone have increased explosively with the development of the advanced information society. Especially, in a wireless communication system the applied frequency band shifts increasingly to a high frequency range by the requirement to higher speed and higher density communication.
In order to speed up the signal transmission velocity, the reduction of delaying time for the propagation of signals is an important subject, and therefore a reduced dielectric constant applied for the information and telecommunications equipment becomes indispensable. Also, in the high frequency range, since the high frequency has a property to lose by converting in the form of heat, in order to transmit electric signals effectively, a material having a small dielectric loss (dielectric constants ∈×dielectric dissipation factor tan δ) is necessary so that a reduced dielectric constant of a material is, also, required in this respect.
Namely, for plastic components employed for the information and telecommunications equipment, as the electrical characteristics, low levels of the specific dielectric constant and the dielectric dissipation factor are given as important prescribed properties in addition to a solder heat resistance, processability, and dimensional stability. Especially, it is in a substrate material of the portable wireless telecommunications equipment and a fixing or a holding member of transmitter-receiver element that they are strongly demanded. Fluoroplastics and polyolefin are known as plastic materials having especially low level of the relative dielectric constant where, for example, the relative dielectric constants of Teflon® (trade name) and of polypropylene are approximately 2 and approximately 2.4, respectively. However, those plastics have problems with heat resistance, processability and mechanical properties so that the development of plastic materials having the dielectric properties combined with those various properties simultaneously is demanded. On the other hand, the recent further downsizing and weight saving requirement for electronic equipments are demanded more strongly and also, a heat resistance capable of coping with a reflow method which improves packaging density of component in printed-wiring assembly substrate surface is required.
Liquid polyester resins have good processability, excellent dimensional stability, and high heat resistance which is tolerable to the solder reflow compared with other general plastics, and have ideal characteristics as materials for electronic and electrical components. However, most of the conventional liquid polyesters provide the dielectric constant having 3.0 or more, and even if 3.0 or less, the liquid polyesters and liquid polyesters compound having an excellent balance of processability, heat resistance, reduced dielectric constant, and reduced dielectric dissipation factor to satisfy the requirement of the above mentioned electronic and electrical industrial fields have been unknown.
A molded product of liquid polyester is made generally from a composition compounded with inorganic fillers and the dielectric dissipation factor improves by compounding general fillers while the relative dielectric constant increases. In order to decrease the relative dielectric constant of the molded product, a method is considered to compound spherical hollow material fillers containing air which has the reduced dielectric constant. However, if the product for electronic part having a portion of thickness less than 0.5 mm is produced by injection molding method, compounded hollow filler may be destroyed so that the compounded effect is deprived and the improvement effect of the relative dielectric constant is reduced.
An object of the present invention is to provide the molded product, which has the dielectric property that the conventional liquid crystal polyester has not realized, which simultaneously keeps the heat resistance property such as solder reflow of the liquid crystal polyester, and which is used in the information and telecommunications equipment employed in high frequency band ranges such as microwaves and millimeter waves.